1. Field of the Invention
The present invention relates to an image sensor unit and an image reading apparatus using the same. In particular, the present invention relates to an image sensor unit capable of accurately positioning a light source with respect to a light guide and an image reading apparatus using the same.
2. Description of the Related Art
Typically, copiers, image scanners and facsimiles are known as image reading apparatuses. These image reading apparatuses employ a contact image sensor unit (CIS: Contact Image Sensor) capable of optically reading image information of a document and converting the information into an electric signal. The contact image sensor unit includes an LED module having a light emitting element, such as LED, for illuminating a document, and a light guide that guides light emitted from the LED module and performs linear illumination. Typically, the LED module and the light guide are attached to a frame and are configured into a unit.
The light guide is formed of a transparent member having a length corresponding to the width of a document to be illuminated. In the light guide, a side end surface is a light incident surface on which light from the LED module incidents, and one surface along the longitudinal direction is a light ejecting surface for ejecting incident light. Thus, the light emitting element of the LED module is required to be arranged so as to be faced to the light incident surface of the light guide. However, since the light guide has a narrow shape, the light incident surface is smaller in area than the light ejecting surface. Accordingly, in a contact image sensor unit, it is difficult to accurately dispose the light emitting element of the LED module on the light incident surface of the light guide. If the light incident surface of the light guide and the light emitting element are disposed in a manner deviating from each other, the amount of light emitted from the light emitting element and incident on the light guide decreases, which causes a problem in that a desired illumination intensity for illuminating the document cannot be attained.
Patent Document 1 discloses a line illuminating device in which three pins for positioning a light emitting element are formed at an end of a light guide casing filled with a light guide or on a side end surface of the light guide and three holes into which the respective pins are inserted are formed on the light emitting element. Such a line illuminating device allows the light emitting element to be positioned with respect to the light guide by inserting the pins on the light guide side into the respective holes of the light emitting element.    Patent Document 1    Japanese Laid-Open Patent Publication No. 2004-146870
The line illuminating device of Patent Document 1 is capable of positioning the light emitting element with respect to the light guide. However, in a case of changing the size of the light incident surface of the light guide or changing the mounting angle of the light guide with respect to a frame, the positions of the pins formed on the light guide side are changed. Accordingly, there is a problem in that the positions of holes of the light emitting element and the respective pins on the light guide side do not match with each other and the light emitting element cannot be accurately positioned with respect to the light guide.
In the line illuminating device of Patent Document 1, the three pins on the light guide side should correctly be inserted into the three holes on the light emitting element. This operation is not easy. Accordingly, there is a problem in that assemblage of the image sensor unit requires effort.